1. Field of the Invention
The present invention relates to a light emitting device and an image forming apparatus and, particularly, to a drive driving a light emitting device, such as a laser diode (semiconductor laser), and an image forming apparatus such as a laser printer and a copying machine mounted with a laser diode as a light source.
2. Description of the Related Art
One type of a light emitting device, for example, a laser diode, has a characteristic in which an optical output arises at a threshold current (oscillation start current) Ith as input current is permitted to increase. When an active region is small, the threshold current Ith is small. Further, the higher the laser diode temperature, the larger the threshold current Ith becomes, so that the ratio of increase of light power decreases above a certain temperature.
The lifetime of a laser diode is typically supposed to be longer when it is used under low temperature. Also, its life is subject to deterioration due to degradation inside a crystal, oxidation on the edge surface of the crystal, and the like.